<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>观察watchers</title>
    <script src="../js/vue-dev.js"></script>
    <script src="https://unpkg.com/axios@0.12.0/dist/axios.min.js"></script>
    <script src="https://unpkg.com/lodash@4.13.1/lodash.min.js"></script>
</head>
<body>
    <div id="app_watch">
        <p>
            Ask a yes/no question:
            <input v-model="question">
        </p>
        <p>{{ answer }}</p>
    </div>
    <script>
        var app_watch = new Vue({
            el: '#app_watch',
            data: {
                question: '',
                answer: 'I cannot give you an answer until you ask a question!'
            },
            watch: {
                // 如果 question 发生改变，这个函数就会运行
                question: function (newQuestion) {
                    this.answer = 'Waiting for you to stop typing...';
                    this.getAnswer();
                }
            },
            methods: {
                // _.debounce 是一个通过 lodash 限制操作频率的函数。
                // 在这个例子中，我们希望限制访问yesno.wtf/api的频率
                // ajax请求直到用户输入完毕才会发出
                // 学习更多关于 _.debounce function (and its cousin
                // _.throttle), 参考: https://lodash.com/docs#debounce
                getAnswer: _.debounce(
                    function () {
                        if (this.question.indexOf('?') === -1) {
                            this.answer = 'Questions usually contain a question mark. ;-)';
                            return;
                        }
                        this.answer = 'Thinking...'
                        var vm = this ;
                        axios.get('https://yesno.wtf/api').then(
                            function (response) {
                                vm.answer = _.capitalize(response.data.answer)
                            })
                            .catch(function (error) {
                                vm.answer = 'Error! Could not reach the API. ' + error;
                            })
                    },
                    // 这是我们为用户停止输入等待的毫秒数
                    500
                )
            }
        })
    </script>

</body>
</html>